Constantine's daughters, Helena and Constantina, were buried in this circular mausoleum built in the 4C and transformed into a church in the 13C. The inner rotunda ambulatory is crowned with a dome resting on twin columns and linked by graceful arcades. Traces of 4C mosaics can still be seen in the gallery vault, which is richly decorated with grape-harvesting scenes, medallion portraits and floral and geometric motifs.